Photocopying machines



July 4, 1967 R. E. c. BISHOP 3,329,076

PHOTOCOPYING MACHINES United States Patent 3,329,076 PHOTOCOPYING MACHINES Robert Edward Charles Bishop, Farnham, England, as-

signor to Admel International Limited, Surrey, England, a corporation of the United Kingdom Filed June 22, 1964, Ser. No. 376,976 Claims priority, application Great Britain, June 26, 1963, 25,414/ 63 4 Claims. (Cl. 95-77.5)

This invention relates to photocopying machinesv Such machines may include two sections, namely an exposure section and a developing section. Arrangements may be made to synchronise the performance of the two sections, or alternatively these may be arranged to function independently, in which case successful two stage operation depends to some extent on operators skill.

The exposure section consists of a revolving glass cylinder around which the original and sensitive paper, for example diazo paper, upon which the ultimate print is produced, are passed together and in intimate contact. A light source, for example a linear mercury vapour discharge lamp together with its associated reflector, is mounted in the glass cylinder. Because of the power levels prevailing in modern lamps, suitable air circulating and/ or ducting arrangements are provided to maintain the cylinder and lamp environment suitable for both the lamp and the process of printing.

The disposition of the lamp and its reflector and air ducts within the cylinder is arranged to provide a maximum arc of illumination for the materials involved in the process compatible with the machine maximum speed and other mechanical aspects. Machines embodying these arrangements are built in a variety of widths up to sixty inches across the machine and it is evidently important that to ensure a satisfactory quality of print certain points require careful attention. It is particularly important that the original upon which the image to be copied is carried, shall throughout its period in the exposing section be in very close contact with the sensitive paper upon which the copy is to be made. To achieve this it is usual to convey both original and sensitive paper around the cylinder by means of travelling bands which may be either narrow or broad to suit a particular design requirement. Such bands are, of course, flexible and may be made in a variety of materials to suit special applications. For practical and mechanical reasons it is necessary that there shall be a space between each of the travelling bands and where there are such spaces the areas or zones registering therewith of the sheets, i.e. the original and sensitive paper carried against the cylinder are in less intimate contact with the printing cylinder than are the areas or zones of the sheets which are in register with the bands. It is also important to achieve and maintain an even temperature across the width of the printing cylinder and such temperature should be relatively low in relation to the characteristics of the sensitive paper being used. Because of the spacing of the travelling bands even distribution of heat across the cylinder width is not always obtained.

Effects not consistent with acceptable quality of result are sometimes apparent when using a machine having a plurality of spaced travelling bands to carry the original and sensitive paper around the glass cylinder. In particular, with certain materials, it sometimes happens that streaks following the spaces between the bands appear on critically exposed sensitive paper passed through the machine, such streaks occurring in the path line thereof.

The exact reason for the formation of such streaks is not clearly understood, but since the effect is similar to unbalanced exposure of the sensitive paper (i.e. a differential darkness in the paper), We have realised that by Patented July 4, 1967 ICC discrete over and under exposure in the areas concerned, the undesirable effect may be eliminated.

According to the present invention, in a photocopying process wherein the original and sensitive paper are carried in contact around a translucent cylinder housing a light source, by a plurality of transversely spaced travelling bands, the sensitive paper is differentially exposed in those areas registering with the bands and those areas registering with the space or spaces therebetween to compensate for the aforementioned differential darkness.

The sensitive paper may be differentially exposed by being over exposed in those areas registering with the space or spaces between the travelling bands compared with the exposure given to the areas registering with the bands.

The differential exposure may be obtained by introducing the areas to be comparatively over exposed to the light source earlier than the areas to be given a normal full exposure; alternatively, the areas to be over exposed may be held before the light source for a longer period of time than are the areas receiving the normal full exposure.

The differential exposure may also be obtained by under exposing those areas of the sensitive paper which register with the space or spaces between the travelling bands in comparison with the exposure given to the areas registered with the bands. For example, the areas to be comparatively under exposed may be held before the light source for a shorter period than the areas which receive a normal full exposure.

Another way of obtaining differential exposure is to vary the light intensity in chosen areas across the cylinder width, whereby those areas to be comparatively over exposed are subjected to a greater light intensity than are those areas which are to be given a normal full exposure.

An embodiment of the present invention is illustrated in the drawing which shows a perspective View of glass cylinder and internally housed light source.

Referring to the drawing, a glass cylinder 1 is rotatably mounted about its axis and housed within the cylinder, parallel to the axis thereof, is a light source 2 in the form of a mercury vapour discharge lamp. To one side of the lamp and also parallel to the axis of the cylinder 1 is a reflector 3 mounted on an air duct housing 4, which is fixed to the main frame, or member thereof, of the machine.

A comb plate 5 is also mounted on the air duct housing 4. This comb plate 5 has a castellated free edge such that there are a plurality of slots 6 spaced longitudinally with respect to the axis of the cylinder 1.

A plurality of travelling bands 7 are entrained around the periphery of the rotatable cylinder 1 and tensioned so as to be biassed against the cylinder surface. These bands have to be spaced apart for a variety of reasons, for example to allow pick-up fingers to engage with the sheets being carried by the bands. The bands 7 and the comb plate 5 are so disposed with respect to each other that the slots 6 in the plate register with the spaces 8 between the bands.

It will be appreciated from examination of the accompanying drawing that light from the lamp 2 and reflected by the reflector 3 falls upon a limited arc of the glass cylinder 1. Thus, depending upon the speed of rotation of the cylinder, sensitive paper carried by the bands 7 against and then with the cylinder is exposed to light for a determined period of time. Because of the castellated profile of the free edge of the plate 5 it will be appreciated that certain areas of the sensitive paper are exposed to light through the slots 6 earlier than are other areas of the paper. Those areas which are first exposed to light register with the spaces 8 between the bands 7 and hence are comparatively over exposed with respect to the remaining areas of the paper, which are given a full normal exposure. It is thus possible to eliminate the appearance of dark streaks which are observed to occur when sensitive paper, such as diazo paper, is exposed in conventional known apparatus.

Instead of locating the comb plate so that areas of the sensitive paper are pre-exposed in chosen areas, the plate may be located at the end of the arc of light with respect to the direction of movement of the paper, so that the areas to be comparatively over exposed are held before the light source for a longer period than are those areas which are given a normal full exposure.

The length of the slots 6 depends upon the degree of over exposure that is desired and this in turn depends upon the sensitivity of the paper being used and the exposure time given to it. It will thus be appreciated that in practice the appropriate slot length must be chosen according to these factors.

What we claim is:

1. Photocopying apparatus including a translucent cylinder, a light source housed within said cylinder, a plurality of transversely spaced conveyor bands entrained about said translucent cylinder and adapted to convey an original and a light sensitive sheet about said cylinders to define areas of light sensitive sheet registered with bands and areas of light sensitive sheet registered with spaces between the bands and tending to produce differential darkness in the areas of light sensitive sheet registered with said bands with respect to the areas registered with said spaces, and means for diiferentially exposing said sensitive sheet to said light source in those areas registered with said bands, with respect to those areas registered with each space between adjacent bands, whereby said differential exposing will compensate for said differential darkness, said means comprising a comb plate housed within said cylinder, having a castellated free edge adapted to cast a castellated shadow along one of the leading and trailing edges of a light zone through which said sensitive sheet passes in its travel about said cylinder, said comb plate being positioned to cast an extended shadow in registry with those areas of the sensitive paper requiring less exposure as determined by said differential darkness.

2. Apparatus according to claim 1 wherein said comb plate has projecting parts forming slots therebetween, said slots being in registry with said spaces between said band and said projecting parts being in registry with said bands.

3. Photocopying apparatus including an elongated light source emitting a constant intensity of light throughout its length, a translucent cylinder in which said light source is housed, light from said source falling upon a limited arc of said cylinder, a plurality of transversely spaced conveyor bands entrained about said translucent cylinder and adapted to carry an original and a light sensitive sheet about said cylinder, and means defining a castellated profile along one'edge of said arc extending parallel to the axis of said cylinder, the stepping in said castellated profile being respectively in registry with said bands and spaces therebetween.

4. Apparatus according to claim 3 wherein said means defining a castellated profile defines recesses formed therein, said recesses being in registry with the spaces between said bands.

References Cited UNITED STATES PATENTS 2,895,395 7/1959 Gern 77.s

JOHN M. HORAN, Primary Examiner. 

1. PHOTOCOPYING APPARATUS INCLUDING A TRANSLUCENT CYLINDER, A LIGHT SOURCE HOUSED WITHIN SAID CYLINDER, A PLURALITY OF TRANSVERSELY SPACED CONVEYOR BANDS ENTRAINED ABOUT SAID TRANSLUCENT CYLINDER AND ADAPTED TO CONVEY AN ORIGINAL AND A LIGHT SENSITIVE SHEET ABOUT SAID CYLINDERS TO DEFINE AREAS OF LIGHT SENSITIVE SHEET REGISTERED WITH BANDS AND AREAS OF LIGHT SENSITIVE SHEET REGISTERED WITH SPACES BETWEEN THE BANDS AND TENDING TO PRODUCE DIFFERENTIAL DARKNESS IN THE AREAS OF LIGHT SENSITIVE SHEET REGISTERED WITH SAID BANDS WITH RESPECT TO THE AREAS REGISTERED WITH SAID SPACES, AND MEANS FOR DIFFERENTIALLY EXPOSING SAID SENSITIVE SHEET TO SAID LIGHT SOURCE IN THOSE AREAS REGISTERED WITH SAID BANDS, WITH RESPECT TO THOSE AREAS REGISTERED WITH EACH SPACE BETWEEN ADJACENT BANDS, WHEREBY SAID DIFFERENTIAL EXPOSING WILL COMPENSATE FOR SAID DIFFERENTIAL DARKNESS, SAID MEANS COMPRISING A COMB PLATE HOUSED WITHIN SAID CYLINDER, HAVING A CASTELLATED FREE EDGE ADAPTED TO CAST A CASTELLATED SHADOW ALONG ONE OF THE LEADING AND TRAILING EDGES OF A LIGHT ZONE THROUGH WHICH SAID SENSITIVE SHEET PASSES IN ITS TRAVEL ABOUT SAID CYLINDER, SAID COMB PLATE BEING POSITIONED TO CAST AN EXTENDED SHADOW IN REGISTRY WITH THOSE AREAS OF THE SENSITIVE PAPER REQUIRING LESS EXPOSURE AS DETERMINED BY SAID DIFFERENTIAL DARKNESS. 